Wow, great post Daniel! That answers a bunch of questions I had myself - I was thinking RHCP would receive better than a H/V combination but it looks like that is not the case.
73, Bill VE6WK
On 1/22/2015 3:29 AM, Daniel Cussen wrote:
Best info on-line I found here:
http://sv1bsx.50webs.com/antenna-pol/polarization.html
Note the losses of having the wrong circular polarisation from a polarised source are very high. In the real world the antenna may not be perfectly polarised on one end, so difference may not be as great.
One very useful/recommended setup for circular is school contacts on 2 metres with the space station. It is recommended to be able to switch polarisation in the middle of a school contact as sometimes the signal is not direct but reflected off a solar panel. In this case you may need to suddenly switch polarisation.
I have a wimo 2m 6 element X circular antenna with the switching kit. The antenna is extremely light and designed to be mounted at the very rear, to prevent the boom interfering in the signal. I was not that impressed by the elements strength, guessing a bird might be able to bend them by landing on them. The driven element is made from a few parts screwed together. I worry corrosion would quickly make it unreliable. Being limited to 6 elements and quite short a longer linear model may work nearly as good.
http://www.wimo.de/xquad-antennas_e.html
also:
http://www.wimo.de/power-splitter-combiner_e.html#18038
The 70cm model I have heard is much better in that the driven element is stamped rather than assembled so less joins to corrode. Also being smaller the elements are stronger.
The switch box is designed to be mounted on the mast near the antenna meaning only one coax cable per band needs to be ran out, but then you need DC multicore to switch polarisations. You can select V, H, LHCP, RHCP. One downside is that they do not give the option of a control box, so you need to build one by hand. You need to ensure you do not transmit while switching.
All in all it is quite expensive, complicated and messy. Unless you had an inferior setup, and found it lacking I probably would not bother. You only lose 3dB using linear when the source is true circular, so probably not really worth it unless you have maxed out on antenna gain/ receive pre-amps. There are additional losses with switches connectors etc.
I have never seen/used the M2 setup so I cannot comment on this. They definitely seem to have more elements as a possibility.
At least with the switching option you can compare the signal on different polarisations to see if it does help in the real world. You could always try it on one band, then apply it to both bands if you get a big difference.
What do others think?
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